Even though the AHA is gone some of the logistical systems that they initially created seemed to have survived, probably cause they're still getting paid by the Hunt economy, now financed by the mysterious Backers introduced in Desolation's Wake. Supplies are still bought n sold, extractions are still driven out, the Welders and Witches support returning Hunters with equipment and treatment, etc.
The supply wagons are mostly a gamified thing, the lore doesn't acknowledge them except for Antonia Higuera: Veteran's bio mentioned that they're abandoned.
The other Hunter's Associations haven't been mentioned by name yet, they're inferred to exist based on one blogpost describing the HA as a centuries old secret society. Presumably there are European branches that handle their own paranormal problems that aren't as big as the American Incursions, stuff like witches and Black Shucks and the like. Hex Breaker might've come from such a branch as an individual answering a call, but the EHA if it exists hasn't been supporting the AHA at all.
China also seems to have monasteries where they train Hunters as described in Zhuge Liu's lore, that could be their own version of the Association.